Python : Comprehensions

Question

I have a list :

lis = ['a', 'b', 'c', 'd', 'd', 'e', 'e']

I am trying to use comprehensions to get values which are duplicate.

duplicates = set([x for x in lis if lis.count(x) > 1])

This returns :

{'d','e'}

Now I create a list out of above set :

duplicates = list(set([x for x in lis if lis.count(x) > 1]))

I get output as :

['e', 'd']

Why the order changes?

BTW, this is a highly inefficient algorithm. Don't use a `set`, use a collections `Counter`, something like `[k for k,v in Counter(data) if v > 1]` — juanpa.arrivillaga, Oct 28 '21 at 06:48

score 0 · Answer 1 · answered Oct 28 '21 at 06:18

0

set does not guarantee the order, dict does.

>> duplicates = dict.fromkeys([x for x in lis if lis.count(x) > 1], None)

>> duplicates = list(duplicates); duplicates
['d', 'e']

answered Oct 28 '21 at 06:18

Antony Hatchkins

score 0 · Answer 2 · answered Oct 28 '21 at 06:23

0

That's because Set stores the elements in a random manner. Try running this code multiple times and see the outputs.

s = {"a","b","g","f"}
print(s)

answered Oct 28 '21 at 06:23

Python learner

2 Answers2